"VDB allows for the use of an initialPeriod option to calculate
depreciation for the period the asset is placed in service. VDB uses the
fractional part of startPeriod and endPeriod to determine the
initialPeriod option. If both startPeriod and endPeriod have fractional
parts, then VDB uses the fractional part of startPeriod."
I think this is wrong, it seems to say that only the fractional part of
startPeriod is used if both, startPeriod and endPeriod, have fractional
parts given. Instead, both fractional parts should be considered. The
last sentence "If both ..." should be omitted from that paragraph.
In LibreOffice Calc the calculation was corrected, see
including a test case document.